Cannot do slice indexing on RangeIndex with these indexers of type Int64Index

I have troubles with slicing dataframe using a variable returned from pd.Series.index.

For example, in my Guided Project: Predicting stock market. I first found the index of the row at which the Date is “1051-01-03” . Then I want to use this index to extract the next 5 days:

stocks = pd.read_csv('sphist.csv')

#Convert the Date column to datetime and 
stocks['Date'] = pd.to_datetime(stocks['Date'])
stocks = stocks.sort_values(by='Date', ascending=True)

one_year_mark = datetime(year=1951, month=1, day=3)
#Find the index at this one_year_mark
idx = stocks[stocks['Date'] == one_year_mark].index
#I want to print out the next 2 days using slicing 
print(stocks[idx:idx+3])

And I got this error

cannot do slice indexing on RangeIndex with these indexers [Int64Index([250], dtype='int64')] of type Int64Index

The error occured at the last line. I appreciate any feedback